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The basic decision-making circuitry underlying social behaviors
such as fighting and mating is incredibly similar in all
vertebrates, from fish to mammals, new research suggests. These
networks may be 450 million years old, the researchers said.

This means that while the input (whether, for example, it is
sight or smell that the animal uses to find its mate) and output
(how it performs its courtship rituals) may be different, the
process the brain goes through to decide to pursue a certain mate
is the same in many different
species of animals, the researchers said.

"How these animals make decisions about whether to fight and how
much to escalate their aggression may be made at least in part on
pretty similar mechanisms in different species," said study
researcher Hans Hofmann, of the University of Texas at Austin.

"It does make sense when you think about it because if you think
about the tasks that animals have to solve, whether it is dealing
with the risk and challenges of reproductive or other kinds of
opportunities, they are fairly similar across species," Hofmann
told LiveScience.

Vertebrate brains

The researchers examined decades of research on genes known to be
involved in these
social behaviors in 88 species of vertebrates — including
birds, reptiles, fish and mammals — and used slices of their
brains to look at the genes' expression in 12 different brain
regions associated with the social decision-making network.

They analyzed this huge data set to see how similar genes
expressed in this network look across species. While species
within a group – say, reptiles – were expected to be
similar, the researchers also found a large similarity between
even far-ranging species, such as mammals and fish.

While these processing networks seem to be very similar, the
actions that come out are different. For example, some species
may use their eyes to spot a mate, while others rely on
pheromones, which send a signal through the nose. [ Top 10 Swingers
of the Animal Kingdom ]

Whether it comes from the eyes or the nose, the signal that a
mate is present is sent to the social decision-making network,
the researchers found. This network processes the risks and
rewards of mating at that time, and it signals other parts of the
brain as to what to do.

If the animal
courts its mate by flying, swimming or walking, different
motor areas of the brain would be activated by the
decision-making network. What remains the same, in all the
different animals tested, was the network itself.

Human animal

Humans weren't included in the analysis because not enough data
on behavioral genes and samples of human brain were available to
analyze. The researchers are hoping to eventually have that
information and incorporate it.

"My prediction is it will be very similar to other mammals. But
we don't know at this point," Hofmann said. "The human brain and
human
brain function didn't just start a couple hundred thousand
years ago when modern humans appeared.We share a lot of our brain
and brain structure with animals, and apparently this may be true
at a fairly deep level."

One thing that does separate mammals from other vertebrates is
the presence of the central cortex, which adds a layer of brain
between the social decision-making network and behaviors. It's
difficult to say how much input the cortex has into behavior, and
more research is necessary to see how it impacts these behavioral
decisions.